The present invention relates to methods and compositions for use in subterranean frac-packing treatments. More particularly, the present invention relates to methods and compositions for inducing tip screenouts in frac-packing treatments.
Subterranean formations, such as hydrocarbon-producing wells, are often stimulated using hydraulic fracturing treatments. In a hydraulic fracturing treatment, a viscous fracturing fluid is injected into a subterranean formation at a rate and pressure sufficient to causethe formation to break down and produce one or more fractures. Particulate solids, such as graded sand, suspended in a portion of the fracturing fluid are then deposited into the fracture when the fracturing fluid is converted to a thin film to be returned to the surface. These particulate solids, or “proppant,” serve to prevent the fractures from fully closing so that conductive channels are formed through which produced hydrocarbons can flow.
It is often desirable to maximize the length of the fractures created by hydraulic fracturing treatments, so that the surface area of the fractures, and therefore the area serviced by the well, may be maximized. However, in certain frac-packing treatments, particularly in weakly-consolidated, highly-permeable sand formations, it may be more desirable to form short, wide fractures that feature high fracture conductivities. One way of creating such short, wide fractures is with a tip screenout.
In a tip screenout, the growth of the fracture length is arrested when the proppant concentration at the tip of the fracture becomes highly concentrated, typically due to fluid leak-off into the surrounding formation. The concentrated proppant slurry plugs the fracture and prevents additional lengthening of the fracture. Any additional pumping of the proppant slurry beyond this point causes the fracture to widen or balloon and packs the existing fracture length with additional proppant. This results in a relatively short, wide fracture having both a high fracture conductivity and a high proppant concentration.
Design features typically employed in situations in which a tip screenout is desired often involve methods of ensuring that fluid leak-off is high relative to the rate and amount of proppant injection. This can be achieved in a number of ways, including, but not limited to, using a small amount of pad fluid to initiate the fracture, using little or no fluid loss additive, using high proppant concentrations earlier in the treatment, pumping more slowly during the fracturing operation, or some combination thereof. However, even using such methods, pressure transients collected by downhole pressure gauges during frac-packing treatments indicate that tip screenouts often do not occur when and where desired or intended. Instead, the fluid at the tip of the fracture often remains mobile, the fracture tip continues to grow throughout the treatment, and the desired proppant concentration in the fracture is not reached. Because of this, the desired high fracture conductivity may not be obtained.